Process for preparing D,L-Lactide

Abstract

An improved process for the preparation of D,L-Lactide which can be used directly in polymerization reactions.

What is claimed is: 
     
       1. A process for preparing D,L-lactide which comprises a) dissolving D-lactide in a first volume of a solvent or a mixture of solvents capable of forming an azeotrope with water, to produce a first solution;   b) filtering the first solution;   c) dissolving L-lactide in a second volume of the solvent or mixture of solvents, to produce a second solution; d) filtering the second solution; e) combining the filtered first solution and the filtered second solution, to produce a starting solution; f) concentrating the starting solution, to produce a residual solution; g) cooling the residual solution until a crystalline precipitate of D,L-lactide forms; h) separating the crystalline precipitate from the remainder of the residual solution; and i) drying the crystalline precipitate.   
     
     
       2. A process as recited in claim 1 wherein the solvent is toluene. 
     
     
       3. A process as recited in claim 2 wherein steps a)-d) are each conducted at a temperature between about 40° C. to about 70° C. 
     
     
       4. A process as recited in claim 3 wherein steps f) and i) are each conducted at a pressure below atmospheric pressure. 
     
     
       5. A process as recited in claim 4 wherein in step f, the starting solution is concentrated by evaporation. 
     
     
       6. A process as recited in claim 1 wherein the first volume is about equal to the second volume. 
     
     
       7. A process as recited in claim 6 wherein the concentration of D-lactide in the first solution is about equal to the concentration of L-lactide in the second solution.